Convergence apparatus for multi-gun cathode ray tubes



July 1, 1969 s. A. BURDICK 3,453,472

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INVENTOR. GLEN A. BuRv/cK ga /J 51W ATTORNE Y G. A. BURDICK July 1, 1969CONVERGENCE APPARATUS FOR MULTI-GUN CATHODE RAY TUBES I6 of 3 Sheet 11vVENTORT Gmv A. Bz/Rp/cK Filed Jan. 18, 1967 G. A. BURDICK CONVERGENCEAPPARATUS FOR MULTI-GUN CATHODE RAY TUBES Jul 1,1969

Filed Jan. 18, 1967 ERG Y m n An 7 N A u G X United States Patent US.Cl. 313-77 5 Claims ABSTRACT OF THE DISCLOSURE A transverse alignmentassembly utilizing two magnetic field producing means positioneddiametrically opposite each other on the neck of a multi-gun cathode raytube in conjunction with a suitably shaped external pole piece isadjustable to produce transverse motion of one electron beam along aselected horizontal line and to produce transverse motion of theremaining electron beams along the same horizontal line in an oppositedirection to effect the proper superposition of the beams on thephosphor screen in a manner which obviates the need for readjustment ofthe radial convergence assembly.

Background of the invention This invention relates generally to colortelevision receiver systems, and more particularly to improvedconvergence apparatus for the multi-gun cathode ray tubes used in suchsystems.

The cathode ray tubes commonly used in color television receivers have athree gun unitized electron beam source directed toward a screencomprising a multiplicity of triads of red, green, and blue phosphordots located on the front panel of the tube. Positioned between the gunstructure and the phosphor screen is a foraminous metallic shadow maskwith each opening in the mask corresponding to one triad of phosphordots on the viewing panel. In operation, the three electron beams mustconverge at the shadow mask for all deflection angles to assure that thethree pictures produced by the three electron beams are properlysuperimposed at each point and combine to produce a full color picture.

A commonly used method for attaining the proper convergence necessaryfor the reproduction of a color image having good color purity andresolution utilizes a gun assembly having the electron guns positionedsuch that their axes intersect at the proper static convergence point. Amagnetic beam convergence assembly positioned on the exterior of thepicture tube neck provides dynamic convergence operation in accordancewith the beam position at a given instant and in addition providesadjustments which permit compensation for errors in beam alignment. Thisassembly provides individual radial motion for each of the threeelectron beams. There also must be provided a component of motion atright angles, i.e. transverse motion, to the radial motion for at leastone electron beam, since random beam misalignment cannot be correctedsolely by radial motion.

While a number of methods have been devised and utilized to provide thedesired transverse motion adjustment of one of the electron beams, theyhave generally proved to be unsatisfactory. In some cases, thetransverse adjustment mechanism requires a substantial amount ofmagnetic field direction, or shielding, within the tube so that only theone electron beam will be affected by the adjustment mechanism. This, ofcourse, results in an increased tube cost, and further it has been foundin practice that the internal shielding is not completely effective sothat resulting fringe fields adversely affect the other electron beams.Still other alignment devices have been found to be effective only onpicture tubes which have been constructed with extreme accuracy wherethe misalignment to be corrected is relatively small, since they deflectthe diverse portions of each electron beam in an inhomogeneous manner,thus distorting the electron spots and degrading picture resolution.However, where picture tubes are manufactured in large quantities, it isdifficult and costly to maintain such standards of extreme accuracy, yetit is still necessary that the manufactured tubes have satisfactoryconvergence, purity and resolution charac teristics.

Objects and summary of the invention Accordingly, it is an object ofthis invention to provide convergence apparatus of economical designwhich overcomes the foregoing difficulties to thereby achieve a picturetube assembly with highly satisfactory image reproductioncharacteristics at minimum cost.

Another object of this invention is to provide convergence apparatuswhich minimizes both the amount and the inhomogeneity of the deflectionof the electron beams, thus minimizing spot distortion and resultantloss of resolution.

Still another object of this invention is to provide congergenceapparatus which does not require internal tube shielding to eifecttransverse beam alignment.

A further object of this invention is to provide convergence apparatuscapable of correcting transverse beam misalignment of one electron beamin a color picture tube without adversely affecting the relativealignment of the three electron beams in the picture tube.

These and other related objects are achieved in one as pect of theinvention by the provision of an electron beam convergence assemblyadapted to be mounted upon the exterior of the picture tube neck.Individual radial convergence devices are provided for each of the beamsof the multiple gun structure. To accomplish the transverse beamalignment, two opposing magnetic fields are established within the neckof the picture tube in a manner such that the first magnetic field issubstantially vertical with respect to one electron beam and the secondmagnetic field of opposite direction is substantially vertical withrespect to the remaining electron beams. Means are provided foradjusting these opposing magnetic fields such that only transversemotion of the electron beams will result.

Brief description of the drawings FIG. 1 is a sectioned plan view of acolor cathode ray tube and its associated components;

FIG. 2 is a diagrammatic representation of the devices which produce,control and converge the electron beams;

FIG. 3 is a diagrammatic representation of a radial convergence deviceand its relation to the electron beams from the electron guns;

FIG. 4 is a diagrammatic representation of a purity magnet device andits relation to the electron beams from the electron guns;

FIG. 5 is a diagrammatic representation of a transverse alignmentassembly according to the invention and its relation to the electronbeams from the electron guns;

FIGS. 6, 7, and 8 represent diagrammatically the magnetic fielddirections and magnitudes at each electron beam produced by the magnets,individually and collectively, of the transverse alignment assembly; and

FIGS. 9 and 10 illustrate diagrammatically one method of attainingproper convergence in accordance with the present invention.

Description of the preferred embodiments For a better understanding ofthe present invention, together with other and further objects,advantages, and

capabilities thereof, reference is made to the following disclosure andappended claims in connection with the above-described drawings.

Referring now to FIG. 1, there is shown a multiple gun cathode ray tube11 of the type commonly employed in color television receivers. The tubeconsists of a face plate 13, a funnel portion 15 and the tube neck 17which is terminated with an electrical connector base 19. Deposited onthe face plate 13 is the phosphor screen 21 consisting of a multiplicityof triads of color phosphor dots. Mounted within the tube 11 in spacedrelationship with the phosphor screen is a foraminous shadow mask 23. Adeflection yoke assembly 25 which produces the vertical and horizontalscanning of the electron beams is mounted on the exterior of the neck 17in close proximity to the funnel portion of the cathode ray tube 11. Theadditional apparatus mounted on the neck of the tube consists of aradial convergence device 27, a purity magnet 29 and the transversealignment assembly 31. The radial convergence device 27 operates inconjunction with the transverse alignment assembly 31 to converge thethree electron beams to a single desired point in the static convergenceoperation. Effectively, the purity magnet 29 is operative to shift thethree beams in a desired direction so that after passing through theforaminous shadow mask they impinge in substantial superposition upontheir respective phosphor dots.

FIG. 2 shows diagrammatically two electron guns 33 of a multipleelectron gun structure where each electron gun 33 consists of a cathodeelement 41, a control grid 43, a screen grid 45, a focus electrode 47,an accelerating anode 49, and convergence pole pieces 51. As illustratedfor a static condition, the beams 53, 54 from the electron guns ideallyconverge at an opening in the foraminous shadow mask 23 such that eachbeam will excite only its respective phosphor dot of the screen on thepanel 13. As illustrated, the radial convergence device 27 is mounted onthe exterior of the neck of the tube proximate the convergence polepieces 51 of the electron guns, the purity magnet 29 is mounted near themid-portion of the focus electrode 47 and the transverse alignmentassembly is mounted near the end of the focus electrode 47. In general,the radial convergence device 27 must always be mounted proximate theconvergence pole pieces, but the purity magnet 29 and the transversealignment assembly 31 may be mounted in any position which affordsmaximum control over the electron beams from the electron guns 33. Inthe aforementioned ideal situation, with the electron guns preciselymounted with respect to one another and the foraminous shadow mask inthe cathode ray tube, the electron beams would properly converge at themask during static operation so that the purity magnet, the transversealignment assembly and the static radial convergence adjustment would beunnecessary. As a practical matter, such a precise assembly is notpossible and therefore the corrective devices must be utilized to attainthe proper beam alignment.

FIGS. 3-5 illustrate diagrammatically the manner in which each of thecorrective devices of the alignment apparatus control the electron beamsof a three electron gun cathode ray tube wherein the gun structures 33are spaced 120 apart from one another. In each instance the correctiveaction is affected by varying the strength or direction of the magneticfields indicated by the dotted lines, with the motion imparted to theelectron beams 53, 54 indicated by arrows.

FIG. 3 illustrates diagrammatically the radial forces exerted on theelectron beams 53, 54 by the radial convergence device 27. Theseelectron beams emerge from the vicinity of the center of theirrespective electron guns 33 and enter the magnetic fields establishedbetween their respective convergence pole pieces 51. In operation themagnets of the radial convergence device 27 are individually controlledso that the radial position of each beam 53, 54 is in pendentlycontrolled over the entire 4 scanning raster. The directions of therespective magnetic fields existing between the convergence pole pieces51 associated with each beam determines whether the beams will bedeflected radially toward or away from one another.

FIG. 4 illustrates the manner in which the purity magnet 29 is operativeto control the direction of the electron beams 53, 54. Typically, apurity magnet consists of a pair of washer-like magnetic piecessurrounding the neck 17 of the cathode ray tube. The purity magnetprovides a fairly uniform field across the interior of the neck of thecathode ray tube and exerts substantially equal deflection forces, bothwith respect to direction and magnitude, on each of the electron beams.Axial rotation of the purity magnet 29 changes the direction of themagnetic field within the neck of the tube and changing the relativepositions on the pair of washer-like magnetic pieces with respect to oneanother operates to vary the magnitude of the magnetic field.

FIG. 5 illustrates one embodiment of the transverse alignment assembly31 according to the invention which comprises a support member 61 ofpermeable magnetic mtaerial adapted to be mounted on the neck 17 of thecathode ray tube. The support member has a first Support 63 containing afirst magnet 65. Directly opposite the first support is a second support67 containing a second magnet 69. The support member in the region ofthe second support forms an extended pole piece for the second magnetsuch that the magnetic field emerging therefrom is relatively wide ascompared to the magnetic field emerging from the first magnet 65. Themagnets 65 and 69 are inserted in their respective supports with likepoles of each magnet adjacent the neck 17 of the tube (as shown withboth north poles adjacent the neck of the tube). The support member ispositioned on the neck of the tube such that the first magnet 65 isdisposed directly above one of the electron guns 33 and the secondmagnet 69 is disposed below and equidistant from the remaining twoelectron guns.

In effect the transverse alignment assembly 31 illustrated in FIG. 5establishes a relatively narrow magnetic field which is substantiallyvertical in the area of an electron beam 53 from one electron gun andestablishes a relatively broader second magnetic field of oppositepolarity which is substantially vertical in the regions of the electronbeams 54 of the two remaining electron guns. FIGS. 6, 7, and 8illustrate the manner in which the individual magnets 65 and 69 of FIG.5 cooperate to provide the desired magnetic fields in the regions of theelectron beams 53, 54. As seen in FIG. 6, the magnet 65 is operative toproduce a vertical magnetic field component in the region of theelectron beam 53 and also produces magnetic field components of smallermagnitude in the regions of the electron beams 54 with the lattermagnetic fields being directed outwardly at an angle from the vertical.Referring further to FIG. 7, the magnet 69 in cooperation with thepermeable member 61 operates to produce magnetic field componentsdirected inwardly from the vertical in the regions of electron beams 54and also produces a smaller vertical magnetic field component intheregion of electron beam 53. As indicated by the direction of the arrows,the direction of the magnetic field components produced by the magnet 69are opposite to the direction of the magnetic field components producedby the magnet 65.

As shown in FIG. 8, the magnetic field components of FIGS. 6 and 7combine to produce resultant magnetic fields which are substantiallyvertical in the regrons of the electron beams 53, 54 with the field inthe region of electron beam 53 being in a direction opposite to thefield in the regions of the electron beams 54. The magnitudes of therespective magnetic fields can be changed by adjusting the positions ofthe magnets 65 and 69 in their respective supports 63 and 67. However,it is found that the directions of the magnetic fields in the regions ofthe electron beams 53, 54 remain substantially vertical over a widerange of such adjustments. The gross directions of the magnetic fieldsmay be changed by reversing the positions of the magnets in theirrespective supports, i.e., by placing the south poles of both magnetsadjacent to the neck 17 of the tube.

FIGS. 9 and 10 illustrate one simplified method of attaining convergenceas provided by the present invention. For this illustration it isassumed that the hollow circles labeled B, R, and G represent theinitial positions of the beams from the three electron guns on theshadow mask. First, as shown in FIG. 9, through the use of the radialconvergence device 27, the R and G beams are brought to a point ofconvergence and the B beam is defiected so that it lies on the samehorizontal line 71 as the converged R and G beams. Then, as shown inFIG. 10, by suitably adjusting the magnets 65 and 69 of the transversealignment assembly 31, the converged RG beams and the B beam are broughtto convergence along the horizontal line 71 thereby forming theconverged BRG beams. Since the fields produced by the magnets 65 and 69remain substantially vertical in the regions of the electron beams 53,54 over a wide range, the electron beams are restricted to horizontalmotion over this range as the transverse alignment assembly 31 isadjusted, thereby maintaining convergence of the previously converged Rand G beams and eliminating the necessity for readjustment of the radialconvergence device 27.

While the inventive concept of a transverse alignment assembly providingopposing magnetic fields which are substantially vertical in the regionsof the electron beams of a multi-gun cathode ray tube has been describedin conjunction with one specific embodiment, it will be obvious thatthere are many alternative forms the invention could take. For example,the magnets 65 and 69 could be electromagnets rather than permanentmagnets or could take other forms such as cylinders magnetized across adiameter and rotatable to vary-the field strength. If cylindricalmagnets, magnetized across a diameter, are used, they must be fixed inposition relative to the cathode ray tube, with the cylinder axesparallel to each other and parallel to the tube axis. As anotherexample, the extended pole piece associated with the magnet 69 could bean integral part of the magnet and move with it. Also, it can beappreciated that there are many possible variations in the mechanicalsupport member 61 used for holding the the magnets in the properpositions. Other changes and modifications within the scope of theinvention will be readily apparent to those skilled in the art. It istherefore intended that the invention not be limited to the specifics ofthe foregoing description, but rather is to embrace the full scope ofthe following claims.

I claim:

1. In image reproduction apparatus including a cathode ray tube havingan envelope with a face panel, a circular neck portion, an imagereproduction screen formed on the inner surface of said face panel and aplurality of electron gun structures disposed in said neck portion witheach of said electron guns providing an electron beam directed toimpinge upon said screen, apparatus for controlling the relativepositions of said beams in a transverse direction, said apparatuscomprising:

first magnetic field producing means mounted on the exterior of the neckportion of said cathode ray tube directly above a first one of saidelectron guns with a magnetic pole of first polarity positioned adjacentthe neck portion of said cathode ray tube and a magnetic pole of secondpolarity positioned away from the neck portion of said cathode ray tube;and

second magnetic field producing means mounted on the exterior of theneck portion of said cathode ray tube directly opposite said firstmagnetic field producing means with a magnetic pole of first polarity ofsaid second magnetic field producing means positioned adjacent the neckportion of said cathode ray tube and a magnetic pole of second polaritypositioned away from the neck portion of said cathode ray tube.

2. The invention according to claim 1 additionally comprising means foradjusting said first and second mag netic field producing means tothereby vary the magnitudes of the magnetic fields produced in theregions of said electron beams.

3. In image reproduction apparatus including a cathode ray tube havingan envelope with a face panel, a circular neck portion, an imagereproduction screen formed on the inner surface of said face panel andthree electron gun structures disposed in said neck portion with each ofsaid electron guns providing an electron beam directed to impinge uponsaid screen, apparatus for controlling the relative positions of saidbeams in a transverse direction, said apparatus comprising:

a support member of permeable material having first and second magnetsupports on opposite sides thereof, said support member mounted on theexterior of the neck portion of said cathode ray tube with said firstmagnet support positioned directly above a first one of said electronguns; and

first and second magnets mounted respectively in the first and secondmagnet supports of said support member with like magnetic poles of firstpolarity of each of said magnets positioned inwardly toward the exteriorof the neck portion of said cathode ray tube and like magnetic poles ofopposite polarity of each of said magnets positioned outwardly away fromthe exterior of the neck portion of said cathode ray tube.

4. The invention according to claim 3 additionally comprising means foradjusting said first and second magnets in said first and second magnetsupports, respective ly, to thereby vary the magnitudes of the magneticfields produced in the regions of said electron beams.

5. The invention according to claim 3, wherein said support memberadditionally comprises an extended pole piece in space-d relation withsaid second magnet support, said extended pole piece cooperating withsaid second magnet to produce an extended magnet field emergingtherefrom in the direction of the electron beams emanating from theelectron guns within the neck portion of said cathode ray tube.

References Cited UNITED STATES PATENTS 2,717,323 9/1955 Clay 313772,898,493 8/1959 Burdick 315-13 X 2,907,915 10/1959 Gleichauf 315132,975,325 3/1961 Gundert et al. 31513 3,188,508 6/1965 Thomas 315-13 XRODNEY D. BENNETT, JR., Primary Examiner. MALCOLM F. HUBLER, AssistantExaminer.

